Assessment of Tailings Ponds by a Combination of Electrical (ERT and IP) and Hydrochemical Techniques (Linares, Southern Spain)

Accumulated mine waste in certain locations in the abandoned mining district of Linares-La Carolina (southern Spain) contain high levels of metals. Therefore, in recent years, many of these tailings ponds have been restored and sealed. This study assessed the efficacy of two geophysical techniques, electrical resistivity tomography (ERT) and induced polarisation (IP), combined with hydrochemical studies, as tools to image the effectiveness of the encapsulation. In the bedrock, ERT profiles distinguished a surficial layer of moderate-low resistivity values (below 80 Ω m), associated with alluvial sands or altered granite, and a deeper zone of high resistivity (up to 1000 Ω m) related to unaltered granite basement. Lateral changes in resistivity were identified inside the upper layer and downstream of the tailings pond. The IP profiles detected local anomalies in the chargeability values (up to 8 mV/V), unusual in granitic rocks. The locations with high chargeability also had low resistivity, which typically indicates the percolation of mining leachates in the underlying altered granites. Integration of geological and geochemical information confirmed this interpretation. This work verified that the combined use of ERT and IP methods were effective for monitoring ancient tailings ponds and for assessing tailings encapsulation.